1. Field of the Invention
The present invention relates generally to building ventilation and more specifically to passive ventilation of buildings.
2. Description of the Related Art
Many buildings are ventilated with so-called “active ventilation” or “mechanical ventilation” apparatus, which typically involves the use of mechanical devices such as fans, air conditioners, etc., which create a forced flow of air through various ducts and vents of the building. In many cases, it is desirable to avoid active ventilation in order to reduce energy requirements.
So-called “passive ventilation” involves an arrangement of vents within a building, without mechanical devices that create a forced flow of air. For example, roof-vents are often placed within the roof of a house to permit airflow between the attic and the house exterior. FIG. 1 shows a house 1 including exterior walls 2, a floor 3, a ceiling 4, and a roof 5 such that an attic space 7 is defined between the ceiling and the roof. The roof includes roof-vents 6, which allow for ventilation of the attic space 7. While this permits ventilation of the attic, the remainder of the house is usually not passively ventilated because the attic is closed off from the rest of the house.
In some cases, passive ventilation has been used outside of the context of only the attic. Some buildings, particularly European homes, employ “passive stack ventilation,” in which the house includes “stack vents” (i.e., pipes or ducts) with lower ends terminating in rooms likely to have higher pollutant levels, such as kitchens, bathrooms, and laundry rooms, and upper ends extending vertically through the roof. These stack vents are also sometimes referred to as “soil vents.”
In a typical design employing passive stack ventilation, a room of a building is provided with wall-vents near the lower edges of the vertical walls that define the room, the wall-vents communicating with the exterior of the building. The room also includes an open lower end of a stack vent. The stack vent typically extends upward through the ceiling of the room and eventually through the roof of the building, terminating at an upper open end. The stack vent typically also extends upward through other rooms and/or an attic of the building. Similarly, other rooms may be ventilated with additional wall-vents and stack vents. Air ventilation through the passive stack ventilation system is primarily caused by pressure differences derived from (1) wind flow passing over the building and the upper end of the stack vent, which causes a venturi effect in the stack vents, and (2) buoyancy differences between indoor and outdoor air. If, as is often the case, indoor air temperatures are higher than outdoor temperatures, the warmer and less dense indoor air tends naturally to rise up through the ventilating stack vents. As the indoor air rises, it draws in cooler outdoor air through the wall-vents.
Traditional rural huts in countries such as Thailand use thatched bamboo walls and thatched roofs through which air can flow. Such huts are often raised above the ground with the floors also having openings through which air may flow.
In some buildings, the bottom floor is raised above the ground so that there is an enclosed airspace below the bottom floor. Some such buildings include floor-vents in the floor and other vents to provide for airflow between the building exterior and the airspace below the bottom floor. One design involves a pipe with one end outside the building and another end opening to the airspace below the bottom floor of the building, the pipe extending underground. Another design involves wall-vents in vertical walls extending below the bottom floor.